1. Technical Field
The present invention relates to the packaging of microwaveable food products and more specifically it relates to the packaging of microwaveable half-products.
2. Description of Related Art
Microwave ovens have become common devices used to cook and reheat food products and 95% of all households in the United States own at least one microwave oven. Consequently, there is a large market for microwaveable foods. Microwave ovens cook food products differently from conventional ovens in that microwave ovens emit radio waves (microwaves) at a certain frequency. Polar molecules such as water attempt to rotate with the microwave electric field and ions such as sodium and chloride tend to move linearly back and forth with the microwave electric field. Energy is thereby transferred to the molecules or ions from the electric field. The motions of these molecules are in turn transferred to the other molecules in the food as heat.
One problem with using microwaves for heating or cooking food products is that there is great potential for hot and cold spots to occur. The unevenness of the heating can be microwave dependent due to the variation of electric field within the oven cavity depending upon the type or brand of microwave oven and the wattage of the microwave oven. Further, problems surrounding the unevenness of the heating can be further compounded by a food dependency component due to the different rates of energy absorption by different ingredients within the food and/or the geometry of the food product. Consequently, a need exists for a microwavable package that promotes more even temperature distribution within a microwave oven independent of the brand and wattage of microwave oven.
Many prior art solutions directed towards solving the problem of uneven temperature distribution have been proposed. For example, U.S. Pat. No. 4,132,811 teaches a two-compartment package. One compartment has a food product to be cooked and the other compartment is an expandable vessel with a vaporizable liquid. The package is placed into a microwave and exposed to microwave energy. The liquid volatilizes thereby causing the compartment having the food product to move within the microwave oven. The resultant movement of the food helps to distribute non-uniform microwave energy.
U.S. Pat. No. 4,987,280, assigned to the same assignee of the present invention, is directed towards heating a shelf-stable, low moisture content food product. The '280 Patent discloses placement of a sealed packet having an aqueous liquid with a dielectric material into a sealed package. Upon exposure to microwave radiation, the contents of the sealed packet rapidly volatilize. The packet's design is such that a seal failure will occur when the interior temperature and pressure reach a predetermined point. Upon seal failure, the volatilized contents disperse throughout the sealed package. In addition, the '280 Patent limits its usefulness or scope to foods with less than 5% (by weight) of moisture.
U.S. Pat. No. 6,455,084 is directed towards placing an absorbent pad having a permeable side and an impermeable side upon a food product. The absorbent pad is moistened with purified water and the impermeable side is placed on a food product, such as a frozen tamale. Upon heating in a microwave, the pad shields the food product from direct microwave radiation and serves as a source of steam generation. The patent indicates that the additional moisture from the pad also helps to keep the food product moist.
Additionally, many packages are expressly designed to be used to store and cook microwaveable popcorn. For example, U.S. Pat. No. 5,488,220, discloses a bag for microwave cooking. The '220 Patent is directed towards a package that controls movement of food product (kernels) within a bag during popping in the microwave. The '220 Patent achieves its purpose by preventing formation of pockets or shelves defined by the corner flaps at the gusseted side panels of a bag to avoid or minimize entrapment of kernels in these pockets to increase the yield of popped kernels.
U.S. Pat. No. 4,596,713 discloses a microwave food package for preparing foods such as shelf-stable popcorn containing a packet of food additive or flavoring which is automatically dispersed over the food product when the package is heated by microwave radiation. The '173 patent discloses the packet can be either a separate bag-like receptacle or part of the inner upper center wall of the package. This package is directed towards distribution of flavoring on the food product.
Although there are numerous teachings in the prior art regarding microwave packages, the prior art fails to disclose a solution to the problem of microwave cooking being dependent upon the brand and wattage power of a microwave oven. Another solution to the problem of cooking a food product in microwaves having different wattages is to place directions on a package that are specific to the power of a microwave. For example, a consumer can be instructed to heat a food product in a particular package for some period of time in an 800 watt oven or for a lesser time in an 1100 watt oven. Unfortunately, many consumers do not know the wattage of their microwave oven, increasing the frustration of the consumer upon reading the directions. Consequently, a need exists for a microwaveable food package that can increase product robustness, e.g. a package and method for cooking food products to an acceptable level with the same cooking time range in microwaves having varying degrees of wattage.
Such packaging can be especially helpful for cooking various food products, such as half-products that, unlike microwave popcorn, provide no audio cue that the product is ready. For example, half-products gradually expand upon microwave heating to form puffed pieces. Examples of such half-products are disclosed in U.S. Pat. Nos. 4,251,551 and 4,409,250. The package should prevent condensation or dew upon the food product during storage and cooking and should be economical to manufacture. The package should be capable of keeping the enclosed food product shelf-stable.